A well-known method of fraud associated with coin-operated machines involves attaching string or thread to a genuine coin and then inserting the coin into the machine while holding the string. Once the coin has passed the validating section and caused an appropriate amount of credit to be accumulated, the user is able to stop the coin from passing into a storage section by use of the string. He can then operate the machine to obtain goods or services, and then retrieve the coin, for example, by pressing an escrow return button.
U.K. Patent Application No. 2,250,622 in the name of the present applicant provides a solution to this problem, wherein the presence of a thread under tension or the presence of a thick thread is detected.
It would be desirable to provide another means of avoiding such fraud and one which does not depend on a user applying tension to the trailing thread.